Telegraph repeater



July 19, 1949. R. B. HEARN ET Al. 2,476,864

TELEGRAPH REPEATER Filed Sept. 29, 1944 2 Sheets-Sheet 1 FIG FOLAR/ZED ATTORNEY July 19, 1949.

R. B. HEARN ET AL TELEGRAPH REPEATER Filed Sept. 29, 1944 IIIIIh POLAR- III (239 IZE 2 Sheets-shew: 2

R. B. HEARN lA/VE/VTORS A. KRECEK AT OR/VEV Patented July 19, 1949 TELEGRAPH REPEATER Richard B. Hearn, Hollis, and Joseph A. Krecek, New Rochelle, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 29, 1944, Serial No. 556,352

18 Claims.

This invention relates to telegraph repeaters and particularly to electronic regenerative repeaters.

An object of the invention is to control the retransmission of Signals by selectively operable electronic means with complete assurance of proper selection as between two or more such electronic means.

Another object of the invention is to eliminate all possibility of false selection as between two or more selectively operable electronic means which might result from interaction among their selection circuits.

Another object of the invention is to isolate signal retransmitting means from electronic selecting means so as to provide for indirect control of the former by the latter.

The invention features the selective retransmission of marking or spacing signals under the control of gas-filled electron discharge tubes which are jointly conditioned to be fired and are rendered conductive selectively by the selective completion of their anode circuits so that no condition of interaction between the control electrode circuits of the tubes can result in the firing of more than one tube.

The invention also features a simple and convenient arrangement for regulating the biasing current of a polarized receiving relay, and for reversing the biasing current to prevent reflection of repeated signals back into a line over which they have been received.

In accordance with one embodiment of the invention, two telegraph lines interassociated through the repeater include the operating windings of their respective receiving relays and the armatures and marking contacts of their respective transmitting relays. The anode circuit of a normally conductive start-stop control electron discharge tube which is of the gaseous type is completed through the serially connected armatures and marking contacts of the receiving relays and through the armature and normal contact of a switching relay. The discharge tube, when conductive, holds in inactive condition an oscillator. Upon operation of either receiving relay to spacing in response to a spacing signal as, for example, the start impulse of start-stop telegraph signals, the anode circuit of the discharge tube is interrupted, quenching the tube, and either of two parallel paths is completed from positive battery through the operating winding of a relay individual to the particular path to the anode, common to the two paths, of a normally non-conductive timing electron discharge tube,

which functions to control the operation of the transmitting relays to spacing, and is preferably of the gaseous type. The function of the relays in the two paths is to isolate from direct control by the timing tube, and to control individually, the two transmitting relays. A similar tube to the anode of which other windings of the two relays are connected in series, functions to control the operation of the transmitting relays to marking.

When the first-mentioned tube becomes deactivated the oscillator breaks into oscillation and oscillates at a frequency of one cycle per'impulse interval of correctly timed telegraph signals and a detector circuit derives timing impulses at the rate of one impulse per cycle. These impulses are applied to the control electrode of the two timing electron discharge tubes previously mentioned. The timing impulse renders conductive the timing tube which has its anode circuit completed through one of the parallel paths to positive battery, this being the tube for controlling the retransmission of spacing signals, and the isolating relay included in this path operates, locks, and operates to spacing the transmitting relay which it is arranged to control, thereby initiating the retransmission of the spacing signal.

Either of the isolating relays, upon being operated to cause operation of its associated transmitting relay to spacing, operates the switching relay to its oif-normal contact. pares a path for eventual completion of the anode circuit of the other timing tube, which is the tube for controlling the retransmission of marking impulses. Upon the application of the next timing pulse to the two timing control tubes, if the receiving relay which had gone to spacing has returned to marking the anode circuit which had been prepared by the switching relay will be completed to positive battery through the reversely poled windings of both of the isolating relays. The isolating relay which has previously operated to cause the retransmission of a spacing impulse will be restored to the initial condition and will reoperate its associated transmitting relay to the marking condition, thereby efiecting the retransmission of a marking impulse. II the receiving relay has not returned to marking when the next timing impulse is applied to the timing tubes, that one of the timing tubes which pertains to the retransmission of a marking signal will not be fired because its anode circuit is not completed except when both of the receiving relays are in the marking condition, and the tim- This relay preing impulses will have no effect on the timin tube which pertains to the retransmission of a spacing signal because this tube remains conderives timing impulses and applies them to the control electrodes of four timing electron dis charge tubes which are preferably of the gaseous type.

connected through oppositely poled marking and spacing windings of the transmitting relay associated with one line to the two contacts of a, selecting relay controlled'by the receiving relay associated with the other line. The other two transmission controlling tubes have their anodes the anode of the start-stop control tube as in the initially described conditiom.

The start-stop control tube will not be fired upon the completion of its anode-circuit because a condenser timing circuit is associated with its control electrode whereby upon the quenching of: the tube its control electrode does not become reconditioned to refire the tube until an interval equal to a complete start-stop permutation code signal. has elapsed. In response to each spacingimpulse of a received code combination the tim-x iugtube pertaining-to the retransmissionof. spacing impulses. will be fired under the controlof.

the; timing impulses and'in response to each marking impulse the timing tube pertaining to the retransmission'of marking impulses will be fired; each of thetubes in turn operating the isolating; relay associated" with the.- receiving'relay' which is responding to the incoming signalsandf the isolating relay in turn operating the transmittingtrelay associated'with the other line and also operating theswitching relay.

' tacts ofa selecting relay controlled by the re-' connected through marking and spacing windings of the other transmitting relay to the conceiving relay on the'opposite side of the repeater.

When either: of the receiving relays is operated to. spacing:- as-i-nl response to the start impulse of a permutation code signal combination it in- I terrupts the anode circuit of'the start-stop con- When; the stop-impulse is received the timing tube pertaining-to the retransmission ofa'marle. lug-impulse will be operated-under the control of the timing impulse'if the last selecting? impulse of the code combination was of" spacing nature:

and; the stop impulse of marking nature will; be. transmitted tothe other: line, orif the last, selecting-impulse of the code combination wascf marking-"nature neither of V the timing tubes will be fired because a marking conditionisalready-being impressed upon the other telegraph line.

to complete the anode circuit. of the start-stop control-1tube; incident to the retransmission of the stop impulse and in the second case the anode circuit of the start-stop control= tube, will have been completed; previously; About the. time. of the. generation of the timing-impulse for the retransmission of the stop impulse the condenser timing circuit conditionsthe control electrode of the start-stop control. tube tofire thetube and the tube fires and stops the oscillator; thus; re-

storing the repeater to theinitial-or steadystater condition, in which it remains until the next start impulse of a permutationcode signal combinationis received.

In accordance with another embodiment oftheinvention each of the telegraph lines includes,- theoperating winding of a receiving relay and the-armature and marking contactof a sending relay as in the previously described embodiment ofthezinvention; Positive'batteryis;seria1ly con--' In the firstcase. theswitching relay will be operated;

nected --through the armaturesand marking contacts of the two'receiving relays to a start-stop control tube which is preferably of the gaseous typeand upon operation of either of, the receiving' relays to spacing the anode circuit of the start-stop control tube is interruptedand the tube is quenched. As in thepreviously described embodiment'of the invention'the start-stop-conv trol. tube-, upon being quenched, sets in opera tion an oscillator from whicha, detector circuit:-

trol tube thereby effecting the starting of the oscillator-and alscj operates its associated selecting relay: to-the' cit-normal or spacing :condition. The selecting relay interrupts the circuitthrough the marking winding of the transmiting relay associated with the: other lin'eto the anode OI'IQHE. ofthe' transmission controlling tubes, thereby quenching that tube, and com pletes a circuit through the spacing-winding of' the; same transmitting'relay to another or the transmission; control tubes;

offthe fouE' iming'tubesthe-tube which has'had its anode circuit completed through the spacing winding of the: transmitting relay'willbe fired and: the. spacing; windingof the-relay will be en"- ergized' to'cperate the armature to spacing and effect the retransmissionof the start impulse of spacingnature. In responseto the first marking selecting impulsaofi the code to be retransmitted;

th receiving relay will be restored to marking,

the selectingirelay wilLberestored to its ncrmal or markingconditionto interrupt the circuit to theanode: of the tube associated with the spacing winding-of the transmitting relay and to lish the anode circuit; of the tube associatedwith the marking winding of thetransmitting relay.

Thetiming; impulse will cause: the firing of this tube and the. flow of current in the-marking wind ing of thetransmitting relay, thereby restoring the relay to marking. In this waymarking and spacing impulses are retransmitted and about the time that the timing impulse pertaining to the stop impulse.- of the telegraph signal combination is generated; a condenser timing associatedwith thestart-stop control tube refires' this tube providing; both of the receiving relays are in thefmarking condition, sothat the anode circuit. of the start-stop control tube has been reestablished and this tube upon being refired stops thercscillator. thusrestoring the system to theinitialcolndition iii-which it awaits the start impulse of the next permutation code combina- 1 tion" to. be retransmitted in regenerative manner. For a complete understanding of the invention reference may be had to the following, detailed description tc'be interpreted in the light of the accompanyingdrawings wherein:

Fig; 1 is a'. schematic circuit diagram showing one embodiment oi; the invention: and

Fig.1 2 is aschematic circuit'diagram showing another embodiment of the invention.

Referring: now; thezdrawings and particularly to Fig.1, a; telegraph line comprising conductors H- and IZ-extends-to a remote telegraph station (not: shown); at: which the telegraph. signaling:

Two of the timing tubes have their anodes" When the timingimpulscs are: appliedto the control electrodes battery is located. Conductor II of the line terminates in the regenerative repeater at the armature of a transmitting relay l3 and conductor I2 extends through the operating winding of a receiving relay I9 to the marking contact of transmitting relay !3. When the line comprising conductors II and I2 is closed at the remote station through the signaling battery, current in the operating winding of relay 54 holds the armature on the marking contact. Current flowing in the biasing winding of relay I4 in a circuit from ground through resistor IS, the biasing winding of the relay, conductor II, winding of transmitting relay I3, conductor I8, armature and lefthand or marking contact of a selecting or transmission. controlling relay I9 and grounded battery 2! seeks to drive the armature of relay I4 to the spacing contact but the operating winding dominates and holds the armature on the marking contact. A third or looking winding of receiving relay I4 is included in a circuit from ground through the locking winding, resistors 22 and 23, varistor 24, conductors 26 and i8 and armature and left-hand contact of relay I9 to battery 2!. Varistor 24 is so connected in this circuit that it presents high resistance to the flow of current from battery 2| so that very little current fiows in the locking winding of relay M and this relay is free to respond to the opening, at the remote station, of the line circuit comprising conductors I I and i2 and to operate its armature to spacing. A condenser 25 is connected between ground and the junction of resistors 22 and 23.

The line circuit over which signals received on the line circuit comprising conductors II and I2 are adapted to be repeated, comprises conductors 3i and 32 which extend to a remote telegraph station at which the battery for supplying signal ing current is located. Conductor 3! terminates in the repeater at the armature of transmitting relay 33 and conductor 32 extends through the operating winding of a receiving relay 3% to the marking contact of transmitting relay 33. The biasing winding of receiving relay 34 is connected in a circuit from ground through resistor 36, the biasing winding of the relay, conductor 3'1, winding of transmitting relay 33, conductor 38, and armature and right-hand or markin contact of a selecting or transmission controlling relay 39 to battery 4| which is connected between the right-hand contact of the relay and ground in the same polar sense as battery 2|.

The circuit of the locking winding of receiving relay 34 extends from ground through the locking Winding of the relay, resistors 42 and 43 varistor 4 3, conductors 4E and 58 and armature and righthand contact of relay 39 to battery 9i. Varistor 94 is connected so as to present high resistance to the flow of current from battery All, so that there is very little current flowing in the locking winding of relay 34 and the relay is free to operate to spacing upon the opening of the line circuit comprising conductors 3i and 32 at the remote station. A condenser is connected between ground and the junction of resistors 92 and 43. From this it will be apparent that the circuits of receiving relays HI and 34 and of transmitting relays I3 and 33' are completely symmetrical. Relay It is adapted to receive signals from the line circuit comprising conductors II and I2 and relay i3 is adapted to transmit signals into this line circuit. Relay 3% is adapted to receive signals from the line circuit comprising conductors 3! and 32 and relay 33 is adapted to transmit signals into this line circuit. Signals may be repeated vacuum tube.

from either line circuit into the other but not in both directions simultaneously. From this it will be apparent that the repeater is in the form generally known as a two-way half-duplex repeater.

A circuit is traced from the positive terminal of battery 5|, the negative terminal of which is connected to ground, armature and marking contact of relay I4, conductor 52, armature and marking contact of relay 34, conductor 53, armature and left-hand contact of a switching relay 54, resistor 56 and conductor 5I to the main anode 59 of a cold cathode gas-filled electron discharge tube 59. The cathode SI of tube 59 is connected to the junction of resistors 62 and 63 which are connected in series between the negative terminal of battery 54 and ground and which comprise a potential divider for establishing the desired potential of cathode 6| relative to main anode 58. In the idle condition of the repeater tube 59 is conductive in its main gap and the cathode 6| of the tube is positive with respect to ground.

The cathode of tube 59 is connected through current limiting resistor 66 to the grid of an electron discharge tube fil' which is preferably a The cathode of tube 61 is connected to the junction of resistors 68 and 59 which are connected in series between the negative terminal of battery I0 and ground. The anode of tube 6? is connected through conductor it and tapped inductance winding I2 to ground. With cold cathode tube 59 conductive as the steady state condition and with the grid of tube tI connected to the cathode of tube 6| the gridto cathode potential of tube 61 will be such that steady current flows in its anode-cathode circuit and through inductance winding I2.

The upper terminal of inductance winding I2 is connected through resistor I3 to the grid of the left-hand triode section of a hot cathode vacuum electron discharge tube I4. The tap or intermediate terminal of inductance winding I2 is connected through resistor I6 to the grid of the left-hand triode section of tube I4 and through resistor II to the cathode. The anode of the left-hand triode section of tube I4 is connected to the positive terminal of battery 18. The inductance winding I2 is shunted by a variable condenser I9. The elements comprising inductance winding 12, condenser 19 and the lefthand triode section of tube I4 and their interconnections will be recognized as an electron tube oscillator circuit. Condenser I9 is preferably adjusted so that the frequenc of the oscillator is twice the telegraph signaling frequency, from which it follows that the duration of each cycle of the oscillator is equal to the duration of one impulse of correctly timed telegraph signals. However, with steady unidirectional current flowing in tube 61 and inductance winding I2 oscillation within the oscillatory circuit will be prevented, energ willbe stored in the magnetic field of inductance winding 12 as a result of the flow of direct current therethrough and condenser I9 will have a small negative charge with respect to ground, this charge being equal to the ohmic potential difference across inductance winding I2 which is the product of the resistance of this winding and the direct current flowing therethrough.

Referring again to tube 59, the cathode 5| and control anode 8| thereof are interconnected through condenser 93 and. resistorBZ connected in series. The junction of resistor 32 and condenser 33 is connected through variable resistor 8A to the positive terminal of battery 86, the negative twin triode tube 92.

acre-see terminals-of which gamiei. .mhciun tionz -t e anode an rid of the right-hand trioldes this section of the tube-op rates asa diode. The

cathode of the rightehanditriode. sectionof: tube Wis connected to the junctiongoi resistors 91 and 88 connected in series'qbetwecnr1Jhe=DO 6 t l.- minal of'battery 89: and; ground whereby the cathode of the. right-hand? section of-1- the tube is adjusted to a. potential, which: is positive with respect to ground. The-left-shand plateoi con,- denser 83 has the same; potential as-the cathode 51 of tube 59 and: the right-hand plate has the same: potential: as the anode of the right-hand triodesection of tube I4 which is positive with respect to ground by' the potential different across resistor 8?- plus the anode-cathode potential difference of the' diode-connected section of tube I4. This potential: is. applied to the control anode 8| of tube 59 through resistor 82. Preferably the control anode is positive with respect to the cathode but the potential. difference between them is considerably less than the ionizing potential of the tube. r

The upper terminalzof inductance winding 12 is connected through resistor: 9| to both grids of a Both cathodes of the tube are connected to the movable contactor of a potential divider 93- which is: connected between positive and negative: batteries 94 and 96, respectively. The right-hand anodeof tube 92 is connected through loadresistor 91 to positive battery 98 and through condenser 99 to the control anode I91 of a cold cathode gas-filled electron discharge tube I92. The control anode of tube I02 is also connected to the junction of resistors I03 and I04 connected in series between ground and negative battery I00. Similarly, the left-hand anode of tube 92' is connected through load resistor I0I to positive battery I08 and through condenser I09 to the control anode -I II of cold cathode gas-filled electron discharge tube H2. The control anode of the tube is also connected to the junction of resistors H3 and H4 connected between ground and the negative-battery H6. 'The cathode III of tube I02" is connected to negative battery H8 and the cathode II9'of tube H2 is connected to negative battery I2I. It will be noted thatthe connections thusfar'd'escribed for tubes I02 and 5 I2 are identical and that they will be controlled identically and simultaneously by tube 92 since both sections of the-tube 92 receive like grid, cathode and anode potentials.

The main anode I26 of tube I02 is connected through condenser I-2I to the cathode of that tube. through resistor I29 to ground-and through resistor I29 to branching paths, one of which extends to the'spacing contact of receiving relay I4 and includesgconductor I'3-I, the middle winding of transmission control relay39 and conductor I3 2, and the other of which extends to the spacing contact of receiving relay 34 and includes con- 7 ductor I33; the gnid'dleyinding of transmission control relay I9 and conductor I34. The main anode Isaof tube I'I. 2 isconnected through condenser I3l' to, the catl' odev of that tube, through resistor I 38 ;toground and through conductor I39, resistor I4 I, lower winding of relay 39, conductor I 32, lower winding. of relay I9 and conductor I43 to the right handcontact-oi switching relay 54. In the idle condition. the armature of relay 54 engages its lett-hand contact and as previously described relays. I4. and 3-4 arein the marking col.

tubes I02; and H2, respectively, will be negative as i no pa cm etsdt battery ndthsse" besre e net enerati Thezrep'eater islset in operation by the reception of the start-impulse of a permutation code sna o.; ture and; er assumed to be received overthe teleg-rapl- 1 inei comprising conductors II and I2, The start impulse is; evidenced by interruption of the current hrough the operating winding of receiving relay I4 and accordingly the biasing,

winding which is.- the middle winding, assumes control ofthe armatureand operates it from the.

inarsing to thespacing contact. As the armature of relay I4 leaves the-marking contact it interrupts the previously traced circuit from battery.-

5-! through the armature and marking contact of receiving relay 34 and through the armature and left-hand contact of switching relay 54 to the main anode of tube 59.. This results in the tube 59. With theflow of current quenching of 7 through tube 59 interrupted the potential of the cathode. 6! of the tube abruptly changes from a positive value with respect to ground to a nega-. tive value-with respect to ground determined by theflow of current from battery 64 through resistors 62 and 63. The grid of tube 61 is simie larly carried negative-with respect to ground to a sufficient value to cut off the flow of current through tube 6?. This 'cuts'oii the flow of direct current through the inductance winding I2 and.

permits the oscillator circuit comprising inductance I2, condenser I9 and the left-hand triode section of tube 14 to break into oscillation. The oscillator circuit is critically damped so that it starts substantially without transients and generates oscillatory potentials at the rate of one cycle per impulse interval of the telegraphsigrials. The oscillatory potential appearing at the upper terminal of inductance winding I2 is applied to both grids of tube 92. I

If the contactor associated with potentiometer 93 is at the mid-point the cathode of tube 92 will be at ground potential. During the positive half cycles the grids of tube 92 will be positive with respect to ground and during thenegative half cycles they will be negative with respect to ground. Thus the current through the two triode sections of tube 92is caused to rise and fall substantially in. phase with the rising and falling potential at the upper terminal of inductance winding I2. difierence across resistors 91 and I0! increases and therefore the potential of the anodes of tube 92 becomes a minimum at the instant of maximum current.

Condenser 99 is normally difference which is the difierence between the potential at the junction of resistors I03 and I04 and the potential of the anode of the-righthand triode section. of tube 92. Similarly, condenser !99 is charged. to a potential difference which is the difference between the potential at.

the junction of resistors H3 and H4. and the potential of the anode of the left-hand triode section of tube 92. If the tube 92 is cutoff at this time or is only slightly conductive the anodes of. tube 92 will be positive with respect to ground by nearly the full voltage of the batteries 98 and 108. The upper terminals of condensers 99 and I09 and also the control anodes 'IOI and III of with respect .to ground by the potential difference across resistors I03 and H3, respectively,

tion, This pulseis of spacing na- As the current rises the potential charged to a potential 98 and I08, respectively, and will be negative toward the control anodes IOI and III of tubes I02 and II 2, respectively. Since the cathodes Ill and H9 of tubes I02 and H2, respectively, are connected directly to the negative terminal of batteries H9 and I 2!, respectively, the control anodes I! and III are less negative than the cathodes I I! and H9, respectively, by the potential difference across resistors I04 and H4, respectively. This potential difierence is insufficient to ionize and break down the control gaps of these tubes.

As the two triode sections of tube 92 are brought to maximum conductivity at the peak of each positive half cycle of the oscillatory potential applied to their grids, the potential of the anodes is quickly reduced to the minimum positive value, thereby impressing a negative pulse through condensers 99 and I99 to the control anodes IOI and III of tubes I92 and IE2, respectively, thereby driving the potential of the control anodes toward orpossibly beyond and more negative than the cathodes Ill and H9 but not sufficiently beyond to develop the control gap breakdown potential between the cathodes and control anodes. Condensers 90 and 99 quickly discharge to the new potential difference between the anodes of tube 92 and the junction of resistors I03 and I04 in the case of condenser 99 and of the resistors H3 and H4 in the case of condenser I09. From the foregoing it will be apparent that the control gaps of tubes I92 and H2 are not fired as the two triode sections of tube 92 rise to maximum conductivity.

As the conductivity of the triode sections of tube 92 decreases in phase with the decreasing oscillatory potential supplied to the grids of the tube the anodes of tube 92 quickly rise to or possibly above their initial potentials. As the rise occurs, a positive pulse is applied through each of the condensers 99 and I09 to the control anodes HM and Ill, respectively, of tubes I02 and H2, respectively. This change in potential of the control anodes HM and I I I is opposite in sense to the previous change and, accordingly, the control anodes are carried toward ground potential and away from the negative potential of the cathodes iii and H9 by an amount sufiicient to fire the control gaps of these tubes. Condensers 99 and I99 quickly recharge in accordance with the reduced conductivity of tube 92 but in the meantime if positive battery has been connected to the main anode of either of the tubes I02 and H2 in a manner which will be described hereinafter, the discharge in the control gap of that tube will transfer to the main gap and thereafter as condensers 99 and I09 recharge the control anodes IOI and III will be carried back to their initial potentials with respect to the cathodes I I! and I I 9 and the discharge in the control gaps will be quenched.

Referring again to the start-stop control tube 59, it was previously stated that in the idle or steady state condition the cathode was positive with respect to ground and that upon' the quenching of the tube the cathode goes negative with respect to ground. The difference between the positive potential of the cathode 6! and the more positive potential of the control anode 8I of tube 59 is considerably less than the control gap breakdown potential. At the instant of the cutting oil of discharge current through tube 59, when the cathode BI of tube 59 is carried negative, a negative pulse is applied through condenser 83 to the control anode 8I of tube 59 and to the anode of the diode connected section of tube I4 and the negative swing of the cathode SI of tube 59 is sufficient to carry these electrodes from their previous positive potential with respect to ground to a potential slightly negative with respect to ground. Immediately current be-- gins to flow through-resistor 84 into condenser 83 to charge the condenser. Resistor 84 is of high value and slows the charging of condenser 83 so that the potential difference across condenser 83 will not reach the control gap firing potential of tube 59 until the selecting pulses of the telegraph code have been received and retransmitted and the retransmission of the stop impulse has been or is about to be initiated. Thus the control gap of tube 59 is fired an interval after the quenching of the tube substantially equal to the interval occupied by a complete telegraph signal code combination including the start and stop impulses thereof. Resistor 84 is made variable to permit adjustment of the charging cycle of condenser 83 to the desired interval.

Returning to consideration of the receiving relay vI4, the armature, having left the marking contact, moves into engagement with the spac-v ing contact and completes a conductive path from positive battery 5| through conductor I32, the middle winding of transmission controlling relay 39, conductor I 3|, resistor i29 to the main anode of timing tube I02. No current flows in this circuit until the control gaps of tubes I02 and H2 are fired by the first positive timing impulse applied through condensers 99 and 99 to the control anodes of those tubes. The discharge cannot transfer to the main gap in tube H2 because the main anode circuit is open at the righthand contact of switching relay 54. However, the discharge transfers to the main gap in tube 102 and current flows in the middle winding of relay 39, driving the armature to the left-hand or spacing contact. Negative battery I46 on the left-hand contact of relay 39 is substituted for positive battery on' the right-hand contact in several circuits. One of these circuits is traced from battery I46 through the left-hand contact and armature of relay 39, conductor 38, winding of transmitting relay 33, conductor 31, middle or biasing winding of receiving relay 34 and resistor 36 to ground. The reverse current caused by battery I46 operates the armature of relay 33 from the marking to the spacin contact, thus disconnecting line conductors SI and 32 and efiecting the retransmission of the start impulse of spacing nature. The reversed current in the middle or biasing winding of relay 34, which previously sought to operate the armature to the spacing contact, now holds the armature on the marking contact. Another path in which the battery polarity has been reversed is traced from negative battery E46 through the armature and lefthand contact of relay 39, conductors 38 and 46, Varistor 44, resistors 43 and 42, and lower or locking winding of relay 34 to ground. Varistor 44 offers low resistance to the flow of current from battery I46 and this current flowing through the lower winding of relay 34 produces a magnetic field which supplements and aids the middle winding in holding the armature of relay 34 on the marking contact. Condenser 45 becomes charged to the potential at the junction of resistors 42 and 43.

Another circuit in which the battery polarity is reversed is traced from negative battery I46 through the left-hand contact and armature of relay 39, upper winding of this relay, conductor 1 current m th re i r :4 t an i s? 4. r nd, R lay. 18 holds} rmaw t on its spacing contact as ja r" u'lt of jt reversal 7 upper winding; Prior tq the fiei tatt e aii l la 2 t it left: and V with positive battery 4 I cg the right-hand contact and r i rf b e e: "a a d t u h. t me er 4! id t c q'w winding of switching relayiiflr this winding plr'c duced a magnetic field "driving the armature to the left hand contact, A njsimil u' circuit is traced from positive battery 2| on theleft 'hai'id contact of relay l9 through the armat ll- 9;'; 1 1 a fdftli mi} .t 6i switching relay 5'4 jto groundg "Ifhe m gnetic field produced by this "current als'o drives the armature enemy 5A to the left hand contact. The upper winding of any 54 is mende circuit, .iro n neg'ative battery s: t ugh ei's Q l i hf .ma 2.,fl j Q7 uc b h c ir fit n t i nd e seek t drive the armature to the "rijht 1; nd contact. W'th magnetic field's pro'duce-d by "middle and lower windings driving theariiiature to th e left-hand contact the upper winding fissubord'ifit to theadditiy'e geffects of t'he two lower ttiii ings and the armature remains a tr e et hand contacts. With current jeversedthrpugh thelower windingas a r'esultcf thefdfleiatihnof relay 39 to its left-hand contact, the magnetic fields produced b jcurrent ir' 1 't'he middle and lower windings oppose and eutraliz -each fother, leaving the upperwindirig fr e'egto move the armature to the right-hand c act and, accord:- ingly, the ,armatureejof relay '4 moves to t hat contact. I This I 'esults in the comp! di a path tram the marking co r'itactjpffri I) r g relayfld through conauct br '52, th; ar at re an marking contact of receiving rela don'ductor relay s3, armature and rifit-hand to ct of l, conductor 'lf43,'1ower tvind ifng;of relay c ductor 1'42, lower windin of r[ y "3g, r sistor m to the mainaiicde [360i timing tube 112.; With reiayha'a d'c ked ts'left h can act and holding transmittin 4 v ing, "ditio'n, recei 'iri'g re'iay M'in'the marhing cdndi and swit-cnmgreiayjs a on its i ht;- hand'contact,jthe arn at e (if, g" l'a-y .4 intaeiimr t t; a receivedniarkingjsignal without disturbing any of the other relays. F

H can return 'to its marking Upon "the return of 'the ar xiiatiire relay 14 to the mark" on Y a received marking) v J a is connected overfa '"revicusiy tacedci rq cluding the armature and liking co act, I g d reeeivm relay 1'4, "the r a ureai' dm H contact of relay 34, the armaturefan ecntatt of switching relay; wihdiiig s of signal are lays l9'and 39in 's'e Y of timing tube 112.; Upon the app i c'at orr of 'the next positive timing impulse thrcugh ctindeiis js 39jandjl09 to thecontrol a dsjfll andj tu esiuz and |2,, esbe ct ofrfthese tubes will 'be fired. I not transfer to the ma ngap cause positive battery Si is 'di thefrnain anbde 126101 this tub contact'ofrelay Iij4. I ,1f'1e to the maingap in tube l ijp'w through,"the 'l ow 'di i in the ,lowerwinding initting' relay 33 and restores that relay to the V marking condition thereby eflecting the retrans mission of a marking impulse. Current is also a reversed through the biasin'glwinding of receiving relay 34, removing the marking bias and resta ing the spacing bias. Current through varist'or to the lower windin'g'ofreceiving relay 34 for-lacking in the marking condition is reduced s'ubstaihtially to'zler'o due to the opposition of; f ered by fvaristor to the flowof current from battery 4|, but condenser discharges through the l'ower winding of relay 34, delaying the rerncval of the holding "current in the marking direction for a short'interval. Current is reversed in the upper winding of signaltran-smission contr"o1- r'e1ay'39, locking this relay with the armature on its'right-hand contact, and current is reversed in the lower winding of switching relay 54, so that the magnetic new produced by the lower winding aids the magnetic field produced by the middlewinding, overcoming the upper winding and restoring the armature to the left-hand centa'ct. The armature ofswitching relay 54 upon leavingthe right-hand contact interrupts thepath to the main anod or tube H2 and queri'ches this tube. "On reaching the left-hand cont'act the armature or relay 54 're'connects' battery}! tu'tne main anode 5a of tube '59. While the selecting impulses are being received and V retransmitted cdnderrser 83 has "not changed sufficir' tlyto-fire the control gap of tube 59 so that tube.

f'spacihg-and marking signals 'cont'inueto'be received tubes 102 and H2 are fired alternately, tube'ltli -for spacing ihip'ulses and tube ll2 for hiarkifiginfpulses to time the retransmission of "thes iiifipuls'e s; Since the timingimpulses which control the tirffir'igtubes J02 and H2 are separated by intervals equal to the impulse intrvails of pr015erly timed telegraph signals, the

tfiansimittirig that aeremams in the marking o'r spacing co'ridition 'for a full impulse interval,

' 'there'hy regenerating a'n'd retransmitting P67 f-ct isi'gn'al's althcugh the signals "received 6y relay "mayhejdistorted. When two successive seating impulses are IeceiVed tube I02 remains I tnauctive in itsihain'gapnm ss and untii'tne armature of reeeivingrelay ill-leaves the spacing 7 contact. 1 Even if the armature of relay [I should leave 'thefspacing "ccntact mbmentarily between two successive spacing "in'ipiilse's fand should quench tuh'e I29, the tube will'be refired f'cr the second '6f the two spacing fimpulsjes "when -the timitigimpulse corre ponding to the secon "(if the two 'si 5ac'ing impulses is impressed upon the e 'ntm i anode 10 or the tube. V The mere quench- 'ingfof tube 126 has no efiectonthe r'eia ysa 'becausethis frela yrmains leclged on its left-hand eontact until tube 1'! 2 is jirle'd and "completes a c i eiiitjf irjfqriv'ng the: armature to the right-- an fibefa t; I

'criductiv 2 does not remain When two successive marking' impulse-s but is quenched as soon as tube II2 operates relay 39 to its right-hand contact which in turn operates the armature of relay 54 to its left-hand contact. Accordingly, tube II2 does not become refired for the second of the two successive marking impulses because its main anode circuit has been interrupted at the righthand contact of switching relay 54 upon operation of the armature thereof to the left-hand contact. However, the quenching of tube II2 has no elfect on relay 39 because it remains locked on the right-hand contact until positively driven to the left-hand contact by tube I02 upon being fired to time the retransmission of a spacing impulse.

The last selecting impulse received by relay I4 is followed by the stop impulse which is of marking nature. If the last selecting impulse has been of spacing nature the armature of switching relay 54 is engaging the right-hand contact and has completed the battery path from the marking contact of relay I4 to the main anode I36 of tube II2. When the timing impulse pertaining to the stop impulse is applied to the control anodes of tubes I02 and H2 both tubes will be fired in their control gaps and the discharge will transfer to the main gap in tube H2 and initiate the retransmission of the stop impulse by operating relay 39 to its right-hand contact whereupon relay 33 will be operated to the marking condition. This will be accompanied by operation of relay 54 to its left-hand contact whereupon battery will be connected to the main anode 58 of tube 59. By the time the main anode circuit of tube 59 has been completed and preferably a little before the completion of this circuit condenser 83 should have become charged sufllciently to fire the control gap of tube 59. As soon as the armature of relay 54 reaches its left-hand contact the discharge will transfer to the main gap, thereby raising the potential of cathode 6! to its initial positive value. This causes the grid of tube 61 to be made more positive with respect to its cathode whereupon the tube becomes conductive and the anode current flows through inductance windings I2 of the oscillator, thereby restoring the oscillator to the original steady state condition and stopping oscillation. The oscillator is critically damped and stops substantially without transients.

When the last selecting impulse of a code combination is marking relay 54 is restored to the left-hand contact before the reception of the stop impulse and the connection of battery 5| to the main anode of tube 59 is completed. As soon as condenser 83 fires the control gap of tube 59 the discharge will transfer to the main gap, tube 81 will be rendered conductive and the oscillator will be stopped. The stopping of the oscillator may occur prior to the application of the timing impulse pertaining to the retransmission of the stop impulse to the control anodes of tubes I82 and H2. This is permissible because it is not necessary to fire the main gap of tube II2 since relay 39 is already engaging its righthand contact and the transmitting relay 33 is transmitting a marking condition to the line circuit comprising conductors 3| and 32. From this it will be apparent that the adjustment of resistor 84 to control the charging of condenser 83 is not too critical. Condenser 83 should fire the control gap of tube 59 a sufficient interval after the generation of the timing impulse pertaining to the last selecting impulse of the code combination to assure that the stopping of the oscillator will not interfere with the production of this timing impulse and before or not later than immediately after the generation of the timing impulse pertaining to the stop impulse. Tube 59 must be rendered conductive in its main gap a sufi'icient interval before the next start impulse is received to assure that the oscillator has been stopped and that a steady state of direct current has been produced in inductance winding I2.

When condenser 83 fires the control gap of tube 59 the control gap potential decreases from the breakdown potential to the discharge sustaining potential, which is between the breakdown potential and the potential applied to the control gap by condenser 83 during idle periods when tube 59 is conductive in the main gap. Due to the sudden positive increase in the potential of cathode 6| of the tube as the discharge current flows through resistor 63, a positive pulse is impressed through condenser 83 before the condenser has an opportunity to discharge, so that the control anode 8| of tube 59 tends to become more positive with respect to ground by the increase of potential of the cathode represented by the potential difference across resistor 63. The positive pulse is also applied to the anode of the diode connected section of tube 14 so that this anode tends to become more positive thereby increasing the conductivity of the diode section. The impedance of the diode connected section of tube I4 is relatively low and accordingly it furnishes a discharge path for condenser 83 so as to prevent the potential of the control anode 8| from rising above a predetermined value with respect to ground. Accordingly, the sudden increase in the potential of the cathode 6| of tube 59 with respect to ground is not accompanied by a corresponding increase in the potential of the control anode 8|. Condenser 83 discharges through the diode connected section of tube I4 to a potential which is less than the discharge sustaining potential of the control gap and accordingly this gap is quenched. The diode connected section of tube I4 establishes a substantially fixed maximum potential for the control anode 8| of tube 59 with respect to ground.

The repeater operates in exactly the same way when signals are received over line conductors 3i and 32 and are to be retransmitted over conductors II and i2. Receiving relay 34 upon going to spacing disconnects battery 5! from the main anode of start-stop control tube 59 due to the fact that the armature and marking contact of relay 34 are in series with the armature and marking contact of relay I4, tube 59 is quenched and the oscillator circuit is set in operation. Upon the reception of spacing impulses the anode circuit of tube E92 is completed through the alternate path including conductor I33, the middle winding of transmission controlling relay I9, conductor i3 3 and the spacing contact and armature of relay 34 and then over conductor 52 and the marking contact and armature of relay it to battery 5|. Relay I9 is operated to its righthand contact over this path, and its armature receives negative potential from battery 20, to operate transmitting relay I3 to spacing, to change the spacing bias current to marking bias current in the middle winding of receiving relay I4, to cause current to flow in the marking direction through varistor 24 and the lower winding of receiving relay id, to lock relay IS on its righthand contact, and to operate switching relay 54 to its right-hand contact by reversing the flow tures of both of relays M and 13d.

7 1 5 zoficurrrent through its smiddle minding s0 this winding opposes (and neutralizes thepe'fiect of the loyier winding. Theretransmissionicf .a

.marking impulse-is effected ;by the-completion of V establishmenttof aflow of current in this sir" cuitdn addition to energizing "1e lower winding ofrela-y lS-andcausing the armature cfthisrelay to be operated to the left-hand contact :also

of relay i -flrwi lrbe operated to the leitehaed contact, "whereby. relay 1-3 will be restored to marking condition andgthe armatureof relay :will be restored to its left-h nd con a t, thereby;

completing the main anode circuit-f 1 111 459 ac-that the discharge will transffir {to zthezmain 'e'nergizesthelower winding of relay 6i; but the V armatureat thistime is engaging the right hand contact to which the lower winding to operate it sothat'theicondition of the armature iof relay-39 is not changed. The reactivation of start-stop control tube 59 and th stopping of the oscillator :is the-same when signals being received over conductors Si andtz aswhen they are being received over line conductors H, and 12.

When signals are being transmitted through the repeater in -one direct-ion from the line conductors ll and 12 to the linecondnctors 3i and =32 a break signal may be transmitted in the opposite direction. The break signal a steady spacing condition and isproduced by in terrupti-ng the closed loop through conductors 3| and 32 and the transmission battery at; the remote station. lf'thewtransm-itting relay 33 should be transmitting a spacing signal over co:-

tductors 3! landtz at the instant that thetransmission of the'break signal towardthe repeater is initiated, "receivingrelay 34 will not respond to the break signall-because it is locked inthe marking condition by the reverse or marking bias through the =nii-ddle -w-ind-ing and by the locking current through-the lowerwinding, all under the controllof relay '39 at this timeon its left-hand contact. As soon as a impulse is ,received -.-over conductors-l l and v 2 by receiving relay I4 and relay tu is operated ,to its right-hand contact and in turn operates relay -33 to marking and removes the locking current from the lower Winding of relay 3% restoresthe spacing bias currentin the middle winding of relay .34, this relay will roperate to spacing and upon theproduction of the next timing impulse -relay l9 will be operated to its right-hand contact and will operate transmitting relay .53 to spacing to ffect the retransmission of the-break signal of spacingnature. Aslong .as the break signal iscoritinued it wil-l be retransmitted over lines l l and iE-andin the meantime =condenser :83 will become .charged vto the breakdown potential of the controlgap of tube 59 and this gap will -be fired. Condensendt will then discharge as the ,potential inthe control gap of the tube'becomes adjusted -.to the discharge sustaining potential .but the discharge will not transfer .to -the. main gap because the armature of relay 54 has been operated toits right-hand contact under the control of relay l9. Whenthe break signal. 'is' terminated by the restoration ofline conductors BI and ,32 to the marking vcondition, receiving .=relay' 34 returns to marking andconnects fbatteryj l fto the main anode of 'tube -l f2. Upon the; generation. of the next timing impulse by .the oscillator the armagap, .tube 18;! Will-be rendered 'rconduct e. and the-oscillator will bestopped.

Thepotentialzdivider:93 which-has its eontactor, 7

connected to "the -:cathodes of detector-tube 8.2 provides .anorientation adjustment 10f the are- 'peater, by which is meant-that ;the instant of firing of the controlgaps of timing tubes I 02 and -l,l:2 -.andther efore the winstar t otoperation of either of the transmitting relays Brand ;3..3imav be varied with respect to :theincoming signals in order to'place the transmitting relays under the control of the :most effective portions of the re- .ceived signal impulses, thereby accommodating therepeater .to various conditionsof signal dis;- tortion. If the contactor is moved leftwardly toward battery ,96 the cathodes will be :made less positive and therefore :thenegative bias on the grids of vtubesoz will be reduced. Under these circumstances-the conductivity of the two triode sections of tube 82 will begin to increase from the minimum 'value earlierlwith respect to :the positive half cyclesof theoscillator and will return to theminimum conductivity later' with respect to the cycles of the oscillator. Tube 924s preferably operated well beyond cut-off --in the negative ,half -;cyc1es of the oscillator and well beyond saturation current in the positive half cycles of the oscillatorysm that in the positive -h-alf cycles cur-rentintube'SZ rises guickly -to saturation :value, remains substantially constant while the ---grid potential esw-ings above saturation value and drops quickly to cut-off; As {the/con- ,tactor of potential divider-83 is moved leftwardly the'current rises to saturation earlier and .decreases tocut-ofi later foreachcycle of theosc'illator, and, accordingly, the positive pulsesapplicd through condensers S9 and 109 to the control anodes of tubes 102 and 1 l2 occur later 'withrespect to received impulses.

mademo'repositiveand thereby the negative-bias on the -gridsof.-tubes-92 is increased. Accordingly, the rise of current tQsatura'tiOn willoccur later and-the decrease to cut-off willoccu-r earlier in eachapositive half cycle-of-theoscillator. In this way the positive impulses :applied through condensers 99 and 109 may be caused to .QQQur earlier with respect to received-impulses. lithe received signals are distorted so that the aroma ture of the receiving relay remains on the mark ing or spacing contacts for lesseninterva-ls than full telegraph. impulse intervals, the contactor of potential divider may be .moved i-leftwardly'or rightwardly until the firing of the control -gaps of tubes {t2 and i l2ris caused to occurwhen the most efiective part of each signaling impulse'jis being received-and therarmaturesof the receiving relayis at rest on the marking .orspacing con- .tact..

Fig. ,2 shows a modified formof ,electroriicrre- V generative repeater which is shown jarranfge'jdior' two paths (comprising one line and :are' f'eceived over. the otherjpath.

Conversely, if the ,contactor is moved rightwardly the cathode The conductors 2H and M2 represent one of the telegraph lines entering the repeater. Conductor 2I2 is connected through the operating winding of receiving relay 2l3, conductor 2, tip spring and normal contact of jack 2H5, conductor 2I1, marking contact and armature of transmitting relay Us and line current adjusting resistor 2I9 to line conductor 2| I. At the remote station, battery is connected to lines 2 and 212, and, receiving relay 2| 3 being a polar relay, the polarity is such that when the circuit is closed at the remote station, the armature is operated to marking by the upper or operating winding, and when the circuit is open at the remote station, the armature is operated to the spacing contact by the current in the lower or biasing winding.

Similarly, the other line entering the repeater consists of conductors MI and 232. Conductor 232. is connected through the operating winding of receiving relay 233, conductor 234, marking contact and armature of transmitting relay 236 and line current adjusting resistor 231 to line conductor 23!. The circuit just traced does not include contacts of a jack comparable with jack 2I6, for reasons which will be set forth hereinafter.

With the repeater in the idle condition, in which the receiving and transmitting relays are in the marking condition, a circuit is traced from positive battery 239 through the armature and marking contact of receiving relay 2|3, conductor 24!, armature and marking contact of receiving relay 233, conductor 242, resistor 245 and the lower winding of a relay 243 and conductor 24!! to the anode of a start-stop control tube 244 which is preferably a grid-controlled gas-filled electron discharge tube. In the idle condition tube 244 is conductive and plate current flows over the path just traced and through the anode-cathode discharge path of the tube. The cathode of the tube is connected to the junction of resistors 246 and 241 which are connected in series between negative battery 248 and ground. Tube 244 has a low and substantially constant anode-to-cathode voltage drop when conductive and the values 01. resistor 245 in the anode circuit and 241 and 245 in the cathode return circuit are such that the cathode is slightly positive with respect to ground when tube 244 is conductive.

The control grid of a tube 25l which is similar to tube 244, is connected to the cathode of tube 244 through resistor 252. The control grid of the left-hand triode section of a twin triode electron discharge tube 253 which is preferably a vacuum tube is also connected to the cathode of tube 244 through resistor 254. The cathode of tube 25! is connected through resistor 256 to negative battery 251 and through resistors 258 and 259 in series 'to ground. The anode of tube 255 is connected through variable resistor 26l and fixed resistors 260 and 259 to ground and through resistor 262 to the control grid of tube 244. A condenser 263 is connected between the anode of tube 25| and the cathode of tube 244.

Since the cathode of tube 244 is slightly positive with respect to ground as previously stated, the grid of tube 25| is also slightly positive with respect to ground. The cathode of tube 25l is negative with respect to ground by virtueof the potential divider comprising resistors 256, 258 and. 259 so that the control grid of tube 25l is positive with respect to the cathode and the tube is conductive. Resistors 25! and 260 are both of high value so that only a very small current is 18 drawn by tube 25L Condenser 263 is charged to the diiierence in potential between the cathode of tube 244 and the anode of tube 251 and the charge on the condenser is positive on the upper plate by virtue of the fact that the cathode of tube 244 is slightly positive with respect to ground and negative on the lower plate by virtue of the fact that the anode of tube 25! is negative with respect to ground by the potential difference across resistor 259 and the total potential difference across resistors 260 and 26f due to anode current through the tube;

The cathode of the left-hand triode section of tube 253 is connected to the junction of resistors 26?"? and 251 connected in series between negative battery 26!] and. ground. Accordingly the cathode of the lef -hand triode section of tube 253 is negative with respect toground. The grid of the lefthand triode section of tube 253 is positive with respect to ground by virtue of its connection to the cathode of tube 244. It follows that the grid to cathode potential is such as to render the lefthand triode section of the tube conductive. The left-hand anode is connected through conductor 289, the left-hand contact and armature of relay 243, conductor 2H and winding of tapped inductance 212 to ground. Since the left-hand triode section of tube 253 is conductive, a steady direct current flows in the inductance 212. The inductance is shunted by a condenser 213 and the inductance and condenser together form an oscillatory circuit which is held in a non-oscillating condition by the direct current through the inductance winding 212, with a small charge on condenser 213 equal to the ohmic potential difierence across inductance 212 and with energy stored in the magnetic field produced by the steady direct current through the inductance winding.

The upper terminal of inductance winding 212 is connected through the resistor 214 to the grid of the right-hand triode section of tube 253. The tap terminal of inductance winding 212 is connected through resistor 21!; to the cathode of the righthand triode section of tube 253. The grid is also connected to the tap terminal of inductance winding 212 through resistor 211. The elements comprising inductance winding 212, condenser 213 and the right-hand triode section of tube 253 and their interconnections will be recognized as an electron tube oscillator circuit similar to the oscillator circuit in Fig. 1. As in the case of Fig. 1, the condenser 213 is preferably adjusted so that the frequency of the oscillator is twice the telegraph signaling frequency, so that the duration of each cycle of the oscillator is equal to the duration of one impulse of correctly timed telegraph signals. The anode of the hight-hand triode section of tube 253 is connected to positive battery 218.

The upper terminal of inductance winding 212 is slightly negative with respect to ground by the amount of the steady potential difierence across inductance winding 212. This negative point is connected through resistor 219 to the grids of both triode sections of a twin triode tube 28l which is preferably a vacuum tube. The cathodes of tube 25!! are connected to ground and the left and right-hand anodes are connected through equal load resistors 282 and 283, respectively, to positive battery 218. With the grids of tube 28l slightly negative with respect to the cathodes, there may be a small discharge current flowing in both halves of the tube and therefore the current flowing through resistors 282 and 283 may cause the anodes of tube 28! to be sli htly less positive than the full potential of battery 218. The right-hand 21 57 &64

29! and 292 to the control grids of tubes 293 and 294, respectively, which are identical with tubes 2 8.3 and 289 and which have their cathodes connected to ground.

The control grid of tube 288 is also connected to the junctionof. resistors 296' and 291 connected in series between negative battery 298 and ground. From this it will be apparent thatthe grid of tube 288 is negative with respect to its grounded. cathode and condenser 286 will be charged to the difference in potential between the potentialat the right-hand anode of tube 28land the potential at the junction of resistors 29.6 and 291. Similarly the control grids of tubes 289, 293 and 294 areconnected to the junction of resistors 3M and 302-, the'junction of resistors 303- and 304-, and the junction of resistors 336 and -1, respectively, which are connected in series. in pairs as enumerated between negative battery 298- and ground. Resistors 296, 301 393 and 306 are of equal value and resistors 29?, 302-; 394 and 301 are of equal value so that tubes 288, 289', 29 3 and 294. have identical negative grid potentials with respect totheir grounded cathodes.

The anode of tube 288 is connected through conductor 31 l, resistor 3|2 and upper winding of relay 2'33 in parallel therewith, resistor 3l3, conductor 3M, upper winding of transmitting relay 218, conductors 3 l6, 3!? and 31.8 and left-hand or' marking contact and armature of relay M9 to positive battery 32L: The anode of tube 289 is connectedthroughconductor 322, resistor 325- and the middle winding. of relay 243 in parallel therewith, resistor 323 conductor 324=,Sthe upper winding of transmitting relay 236,, conductors 326 321 and 328 and the left-hand or marking contact and armature of relay 329 to positive batteryr33l. The anode of tube. 293 is connectedthrough conductor 33.2,. lower winding of transmitting relay 2 I 8, conductors- 333,. 334, 336. and. 33-1 tothe righthand or spacing contact of relay 3&9. The anode of tube 294 is connected through conductor 333, the lowerwind-ing of transmitting relay 236, con.- ductors 339,. 341-, 342 and 3&3 totheright-handor spacing contact of, relay 329.- The: circuit. of the operating winding of relay 319 which includes resistor 345: shunted by condenser 34 is at this time open at. the spacing contact of receiving relay 233 andv the. circuit of the. operating winding of relay 329 which includes. resistor 34.3 shunted by condenser 348 is. open at the spacing. contact of receiving relay 2J3. Thesewindings, when energized, operate the armatures toathe spacing contacts but when. these windings are notenergized,

the armaturesare. held to the marking contacts by current in the biasing windingswhich together with the biasing windings of relays 351. and 352 are connected in series between battery'353 and ground. Thus, the anode circuits of tubes 29.3 and 294 terminate at the spacing contacts of relays 319 and 3.29, respectively, andneither ofithese tubes can bev conductive, inthe idle or steady marking condition. of the repeater. The anode circuits of tubes 283 and, 289. are completed to battery through the marking, contacts and armatures of relays H9 and 329, respectively, and these tubes are. conductive, although their grids are considerablynegativewith respect to their cathodes, the

conductivity being maintained with negativebias on the grid due to the fact'that they are gas-filled tubesand having been fired, they. may notbe quenched under the controi of. their grids. Upon the operationvor one of the "receiving relays, such as the relay 2I-3-, tospacing inresponse to a spacing signal, such asthe start impulse of. a

of tube 251 and the grid; of the left-hand triode section of tube 253 will undergo'a corresponding drop in potential and. iii-the case of tube 251 the new grid potential i "below the firing potential:

The abrupt. decrease in the potential of the oath-- ode oi'tube 224' causes a negative pulse to be I pressed through condenser 233' on "the" anode of tube 251, reducing the anode potential below" the dischargesustaining potential and thus cutting off this tube. In the case of the left-hand triode section of tube 253,1the new grid: potential isbe- Iow the cut-off value" of the tube so that' the flow of direct current through the-anodecircui'tof this tube, which includes the Ieftg-hand con'tactand armature of relay 2 53 andinductance winding 2172', is interrupted. I

Due principally to the small extent to the charge on condenser 21 3', this circuit begins to osciI-lateat aff'requency of one cycle per impulseinterval of telegraph signals and oscillation at uni-form amplitude is maintained by the right-hand triode section of tube 253. The

swing positive in the first half cycle of oscillation ofthe oscillatory circuit which is thepositive half cycle and in each succeeding odd halfcycIe. As 7 the grids swing positive, the flowbf current in both triode sections of tube 281 increases and the anodes become less positive due to the increase in potential difference across resistors 2'82 and 283. As the anodes swingless positive in p0- tential, negative impulses are, applied through condensers 286, 281, "29 l and 292, respectively, to the grids of tubes 288 and 289, 293" and 294, thus decreasing the potential of these grids. with re-' spect to their cathodes. the conductivity of. the triode sections or tube 28 l decreases, in the second half of the positive half cycle of oscilla-.

7 tion the oscillatory circuit, the. anodes of-tube I 28 swing more positive in potential and. positive pulses are impressed. through. condensers 286,28],

29! and 292 on the. controlgridsof tubes 288-,

289., 293 and 294, momentarily carrying thosegrids above the firing potentials with respect. to their cathodes. This occurs once for each cycle of oscillation of the oscillatory circuit.

In themeantime, condenser 263, having applied to. its upper plate the reduced potential of the cathode of tube 244, discharges. The discharging circuit includes .highfixed resistor 260 and high variable-resistor 261- so thatuthe discharging v energy stored in the V magnetic field of 'inductance2T2an'd' also to a 21 of condenser 263 is a character timing operation as will be described later.

Returning again to consideration of relay 2I3, when the armature reaches the spacing contact, it completes the energizing circuit of the lower or operating winding of relay 329 and operates the armature of that relay from the left-hand, or marking, to the right-hand, or spacing, contact. The armature of relay 329 in leaving the left-hand, or marking, contact, disconnects positive battery 33! from a path traced through conductors 328, 321 and 326, the upper winding of transmitting relay 236, conductor 324, resistor 323, the middle winding of relay 243 to the main anode of tube 289, thus quenching this tube and leaving only the tube 288 of the four tubes 288, 289, 293 and 234 conductive. Battery 33! also becomes disconnected from a path through conductors 328, 321, the middle winding of transmitting relay 236, resistor 353, conductor 34!, resistor 35'! and middle winding of relay 352 to negative battery 358. Prior to the disconnection of battery 33! from this path, the resistor 355 limited the current through the middle winding of relay 352 to a value insufficient to overcome the effect of the current in the upper or biasing winding which is holding the armature of the relay on its left-hand contact. A path similar to the one just traced extends from battery 32! through the armature and left-hand, or marking contact of relay 3!9, conductors 3E8 and 3!1, middle winding of transmitting relay 2&8, resistor 359, conductor 334, resistor 36!, and lower winding of relay 352 to negative battery 362. Current in this circuit is kept to a low value by resistor 359 and although the lower winding also seeks to move the armature of relay 352 away from the left-hand contact and therefore adds its efiect to that of the middle winding, the upper or biasing winding dominates the relay. The disconnection of battery 33! from the path through the middle winding of transmitting relay 236 in the middle winding of relay 352 merely interrupts the flow of current in this path.

Battery 33! also becomes disconnected from a path including conductor 328, conductor 363, lower, or biasing winding of receiving relay 233 and conductor 364 to the anode of electron discharge tube 366 which is preferably a vacuum triode tube. The anode of tube 366 is also connected through resistor 361 to positive battery 368, A. path is also traced from conductor 363 through conductor 369 through resistor 31! to negative battery 312, and through conductor 369 and resistors 313 and 314 to negative battery 316. The grid of tube 366 is connected to the junction of resistors 313 and 314. The cathode of tube 386 is connected to the movable contactor of a potential divider resistor 311 which is connected between negative battery 318 and ground.

Prior to the operation of the armature of relay 329 away from its left-hand, or marking, contact, the grid of tube 366 was maintained at a fixed potential dependent on the relative values of resistors 313 and 314 by a flow of current from battery 33! through the armature and marking contact of relay 329, conductors 328, 363, and 369, resistors 313 and 314 to negative battery 316. Biasing current seeking to operate relay 233 to the right-hand or spacing contact was flowing from battery 33! through the armature and marking contact of relay 329, conductors 328 and 353, biasing winding of relay 233, conductor 363, the anode to cathode discharge path of tube 385 to the potential divider comprising resistor 311 connected between the negative battery 318' and ground. The biasing current is adjustable to the desired value by means of potential divider 311, which varies the cathode-to-grid potential of the tube, and thereby varies the anode current.

With battery 33! disconnected from the path tors 313 and 314 to negative battery 316. Dueto the fact that positive battery 368 is connected to the right-hand terminal of the biasing winding of relay 233, whereas positive battery 33! was previously connected to the left-hand terminal, the direction of current flow through the biasing winding of relay 233 is reversed and the biasing winding now operates to hold the armature of relay 233 on the left-hand, or marking, contact to prevent this relay from responding to a spacing signal should such signal at this time be received over lines 23! and 232, and. also to prevent relay 233 from operating to spacing when transmitting relay 236 becomes operated to spacing and opens the circuit through the operating winding of relay 233.

By virtue of the provision of resistor 361 in the path traced from battery 368 through this resistor, conductor 364, biasing winding of relay 233, conductor 369 and resistors 313 and 314 to negative battery 316, the flow of current through resistors 313 and 314 is reduced relative to the current which flowed when battery 33! was connected without intermediate resistance through resistors 313 and 314 to battery 316 and therefore the grid of tube 366 connected to the junction of resistors 313 and 314 is made sufiiciently negative with respect to the cathode that tube 366 is cut ofi. The anode is also made less positive by virtue of the flow of biasing current for relay 233 through resistor 361. The provision of tube 366 in association with the biasing winding of relay 233 provides a simple and convenient means for regulating the current in the biasing Winding of the relay and also for effecting the reversal of the biasing current when relay 329 is operated away from its marking contact.

Upon arrival of the armature of relay 329 on its right-hand or spacing contact, a path from positive battery 33! is traced through conductors 343 and 342, resistor 351, and the middle winding of relay 352 to negative battery 358. Thus the circuit of the middle winding of relay 352 no longer includes high resistance 356, the current in the winding is increased to a value producing a magnetic field which overpowers the field produced by the current in the biasing winding and operates the armature away from the left-hand contact to the unconnected right-hand contact. The left-hand or marking contact is connected through conductor 38! and resistor 382 to the tip spring of a jack 383. Jack 383 has its sleeve grounded and is adapted to receive a plug 384 having connected thereto the selector magnet 386 of a printing telegraph receiving recorder which may be of any desired type, such as, for

example, the telegraph printer shown in Patent 1,904,164 granted April 18, 193-3 to S. Morton et al. The disclosure of the Morton et al. patent is incorporated herein by reference as part of net 385 is intended to symbolize the entire printer,

which may be employed as a monitoring printer; The armature of relay 352 is connected. through conductors 381 and 388 and resistor 389 to bat-'- tery 39!. With the armature of relay 352. on its left-hand or marking contact and plug 384 inserted into jack'383, selector magnet 386 is energized which is the marking condition. When the armature of relay 352 isoperated to spacing by relay 329, the energizing circuit for selector magnet 386 is interrupted and the magnet be-' comes deenergized which is a spacing impulse condition. From this it follows that the fiance tionof relay 352 is to repeat received marking and spacing impulses to the monitoring printer symbolized by selector magnet 386 directly ras received and without being regenerated. By virtue of the connection of the lower winding of relay 352 to the spacing contact of relay 319 which is controlled by receiving relay 233, the relay 352 is adapted to be operated to spacing in response to spacing'sig'nals received over lines 23! and 232 in the same manner that it repeats signals received over lines 2 and 2! 2.

7 Another path is traced from battery 331 through the armature and, spacing contact of relay 329, conductors 343, 342 and 34!, lower winding of transmitting relay 239 and conductor 338 to the anode of tube 294. Thus a path is prepared for the firing of tube 29 when the grid" of that tube shall receive the firing potential through condenser 292 fromthe left-hand triode section of tube '28! under the control of the oscillator. I 7

Another path is traced from battery 33! through the armature and spacing "contactof relay 329, conductors 343, 342 and 34],resistor 358, middle winding of transmitting-relay 235, conductors 321, 393 and 369 and resistor 37! to negative battery 312 and in parallel with this resistor and battery through resistors 313 and 3-14 to negative battery 318. -This represents a reversal of the polarity on the middle winding of relay 236 and Whereas the direction of current in the middle or biasing winding'of relay 236 was previously'in the direction to operate the armature to the spacing contact, the biasing current now flows in-the direction to hold the armature on the marking contact. This is desirable because the flow of current'through the upper winding of relay 236 has been interrupted upon the quenching of tube 299 as previously described and the reversal of bias in the middle winding to 'a marking bias prevents premature operation of transmitting relay 236 to spacing by the biasing winding. 7

Still another'path is traced from positive battery 33! contact of relay 329, conductors 343 and 392 to one terminal of a condenser 393, the other terminal of which is connected tothe junction of resistors 313 and 314' and therefore to the grid" of tube 366. Prior to the operation of the arma tureof relay 329 away from its marking contact, condenser 393' had a potential on its lower terminal which is negative by a few volts with respect to ground, being the difference between the potential of battery 316 and the potential diiTerence across resistor 314 and had a potential on its upper terminal considerably negative with respect to ground, being the difierence between the potential of battery 358 and the potential difierence across resistor 35?. Thereafter, the charge on condenser 393 reverses, the

through the armature and spacing 24 7 upper terminal. becoming positive" with respect to ground to the extent of the full voltage of battery 33! and the lower terminal remaining considerably negative with respect to ground, as previously described.

With the operations lator. The current in the two triode sections of tube 28| rises, to a maximum and then dee creases and as the decrease occurs the potential of the two anodes of the tube increases and posi tive impulses are impressed through condensers 286, 281, 29! and 292 to the control grids of; tubes 288, 289, 293 and 294. Tube 288 is al-' remains in the marking condition under the control of tube 288'. Tube 299 was quenched when the armature of relay 329 left its marking contact and although paths may be traced'froin the anode of tube 289 to positive battery 369 and. also topositive battery 33l,thesfe paths 1m clude relatively high resistances and have connections to negative battery so that the anode of tube 289 is at reduced potential and the tube? will not fire. The anode of tube 293 is also at reduced potential and it will not fire. She anode circuit of tube 294 has been prepared by the operation of the armature of relay 329 to spacing and accordingly this tube fires and energizes the lower windingiof rela 236 thus operating the interrupted, the relay remains in the marking condition because it is held in this condition by the reversed or marking current through the bias ing'winding as previously described. a

If the first significant impulse of the code com-f bination which follows the start impulse should a be of spacing nature, relay 2l3 will remain in the spacing conditionand relay 329 will remain in the spacing condition under the control 'of relay 213. through the anodes of the four tubes 298, 289,--

293 and 234 and when the grids of these tubes are momentarily made more positive by the tim-'- ing impulse, tubes289 and 294 already being conductive, will remain conductive and tubes 289 and 293 will remain quenched.

-If instead the first significant impulse of the code combination should' be of marking natur or when the first marking impulse of the code combination is received over line conductors 2[ l' and H2, relay 2l3 will be reoperated to marking.

' relay 352, thereby permitting' the biasing wind ing of that relay to restore the armature to marking to repeatthe received marking impulse performed by. relay 329 .upon operation to spacing completed, the appa-i ratus awaits the timing impulse derivedby the two triode sections of tube 28l from the os'cil-fl Although the circuit throughthe operating winding of receiving relay 233 is No change will occur in the paths t holding the tube non-conductive.

"to selector magnet 38B of the monitoring printer.

The relay 329 interrupts the anode circuit of tube 294 through the lower winding of relay 236 thus quenching the tube 294, and reestablishes the path to the anode of tube 289 through the upper winding of relay 236 thus preparing for the firing of tube 289.. It reestablishes the positive battery connection directly to the left-hand terminal of the biasing winding of receiving relay 233 and through resistor 313 to the grid of tube 366 and to the lower terminal of condenser 393. With a flow of current reestablished from battery 33! through the armature and marking contact of relay 329, conductors 328, 321, middle winding of relay 236, resistor 356, conductor 34!, resistor 357 and middle winding of relay 352 to negative battery 358, the potential at the left-hand terminal of resistor 35'! applied through conductors 342 and 392 to the upper terminal of condenser 393 goes almost immediately from a positive value with respect to ground of the full voltage of battery 33! to a negative voltage with respect to ground of the difference between the voltage of battery 358 and the potential difierence across resistor 357. Resistor 313 through which positive battery 33! is reconnected to the lower terminal of condenser 393 has a high value and delays return of condenser 393 to its original slightly negative charge, thus The grid of tube 386 is gradually restored to its original potential and when it has been restored normal spacing bias current flows in the biasing winding of relay 233, which is in the anode circuit of tube 366. In this way the restoration of spacing bias on the receiving relay 233 is delayed. Preferably this delay in the restoration of full spacing bias to receiving relay 233 is of the order of a few code impulse intervals but less than a full code combination interval so that the repeater shall not be responsive to momentary interruptions of the telegraph line comprising line conductors 23! and 232 which if permitted to become effective during transmission of signals from the line comprising conductors 2!! and 2!2 into the line comprising conductors 23! and 232 might put the character timing apparatus out of phase with the signals incoming over line conductors 2! l and 2 l2 and result in the multilation of several signal combinations before the character timing circuit should return to proper phase relation to the incoming signals.

As the reception of the impulses of a code combination continues, receiving relay 2l3 follows the received signals and operates relay 329 in correspondence therewith to control selectively the completion of the anode circuit of tube 289 or tube 294. After these paths have been selectively prepared, the tube 28! under the control of the oscillator circuit generates the positive timing impulses so that the impulses of full and uniform length are retransmitted. Following the retransmission of the last significant impulse of the code combination, receiving relay 2l3 responds to the stop impulse of marking nature and returns to the marking condition, or remains in the marking condition in case the last significant impulse of the code combination was of marking nature, and relay 329 is correspondingly operated. If the last significant impulse of the code combination was of spacing nature, tube 294 has been conductive and this tube is quenched and the anode circuit of tube 289 is prepared as relay 329 returns to marking or if the last significant impulse of the code combination was of a ing and impulse timing circuits tors 23! and 232,

Cductors 2!! to the signals and operates relay 3! 9 in corre- 2"6 marking nature, tube 289 is already conductive. When the timing impulse pertaining to the retransmission of the stop impulse is applied to the grids of tubes 288, 289, 293 and 294, tube 289 becomes or remains conductive and relay 236 is operated to or remains in the marking condition to efiect the retransmission of the stop impulse.

Each time that relay 2l3 responds to a marking impulse, it reestablishes the anode circuit of timing tube 244 from battery 239 through the armature and marking contact of relay 2! 3, conductor 24!, armature and marking contact of relay 233, conductor 242, lower winding of relay 243, and conductor 24!! to the anode of tube 244. During the reception of the code impulses, condenser 263 has been discharging to cause the grid of tube 244 to approach the potential of the cathode of that tube but the grid does not reach the firing potential during the reception of the significant impulses of the code so that tube 244 does not become fired incident to the reception of any of the significant impulses of mark ing nature. About the time that the positive impulse for effecting the retransmission of the stop impulse is impressed through condensers 288, 281, 29! and 292, condenser 283 has discharged to such value that the grid of tube 244 reaches the firing potential relative to the cathode and accordingly tube 244 is fired. Immediately upon the firing of the tube the potential of its cathode rises abruptly to the steady state potential which is slightly positive with respect to ground and carries the control grid of tube 25! and the grid of the left-hand triode section of tube 253 to the same potential. The increase in potential of the grid of the left-hand triode of tube 253 restores this section of the tube to conductive state and causes direct current to flow in the inductance winding 272 included in the anode circuit of the left-hand triode section of the tube. This stops oscillation of the oscillatory circuit and consequently the production of positive pulses to fire tubes 288, 289, 293 and 294, and the timing pulse generating circuit awaits the next start impulse and quenching of tube 244. The increase in potential of the control grid of tube 25! causes the firing of this tube and the discharge current flows to recharge condenser 263 to the initial steady state condition. Thus the character timare restored to normal.

When transmission is in the opposite direction, namely, from the line comprising conductoward the line comprising conand 2!2, receiving relay 233 responds spondence therewith, the relays 233 and 3!9 corresponding to the relays 2I3 and 329 respectively. Relay 233 in responding to the start impulse interrupts the anOde circuit of tube 244 and the tube becomes quenched in the manner heretofore described, to start the production of timing impulses. Relay 3!9, upon operating to spacing, interrupts the circuit through the upper winding of transmitting relay 2l8 to the anode of tube 288 which becomes quenched and prepares a. circuit through the lower winding of relay 2 3 to the anode of tube 293 which becomes conductive up on the application of the firing impulse to the grids of the four tubes 288, 289, 293 and 294. Tube 289 remains conductive steadily during the transmission of signals from the line comprising conductors 23! and 232 to the line comprising conductors 2! l and 2!2, tube 294 remains battery 40? and ground. The

27 quenched and the tubes 28'8 and293 are fired alternately for the marking and spacing impulses respectively. Relay 21.8 operated to spacing under the control of its lower winding and is restored to marking under control of: its upper winding, 7

One terminal of the biasing winding of receiving relay 213 is connected through conductor 401 and resistor 432 to positive battery 4113; these elements corresponding to conductor 364, resistor 361 and battery 3158. Likewise the same terminal of the biasing winding of relay 213 is connected to the anode of a vacuum tube 404 which corresponds to vacuum tube 366 'and has its cathode connected to the contactor of potential divider resistor 55% which is connected other terminal of the biasing winding of relay 213 is connected through conductor 6B5, resistor terminal of the biasing winding of relay 213 is also connected through resistors 411 and 412 to negative battery 413 and the junction of resistors 411 and-412 is connected to the grid of tube 404.

Ihe right-hand terminalofthe' biasing winding of relay 213, which is connected through conduc'tor 405 to the junction of resistors 408 and 411 is connected by conductor 414 to conductor 318 over which positive battery connectionfrom battery 321 is suppliedthrough the armature and marking contact of relay 319 for establishing spacing bias in the biasing winding of relay 213 through the discharge path of tube'4e4 as in the case of relay 233 and tube 365. When relay 319 is operated to spacing, this direct battery connection is removed and the current through the biasing winding of relay 213 is reversed, establishing marking bias. The junction of resistors 411 and 412 and the grid of tube 4 04 are connected-to one terminal of acondenser 415, the other terminal of which is connected through conductor 41! to'the spacing contact of relay 319. Condenser 416oper'atesin the same man ner as condenser 393 to delay'the restoration of spacing bias to receiving relay 213 when a spac ing condition impressed on the line comprising conductors 211 and 212 by the repeater is replaced by a marking condition,

It will be noted that the anode circuit of tube 288 which operates transmitting relayi218 to marking, includes the upper winding of relay 24-3 shunted by resistor 312, that the anode circuit of tube 229 which operates transmitting relay 236 I tamer-king includes the middle winding of relay 243 shunted by resistor 3'25, and that the anode circuit of tube 244 includes the lower winding of relay 243. It will. also be noted that'the anode circuit of the left-hand triode section of tube 253 includes the armature and left-hand contact of relay 243. Current in the upper and middle windings produces magnetic f elds urging the armature to the left-hand contact. Current inthe lower winding produces a magnetic field urging the armature to the night-haird contact; With current flowing in the lower winding and in only one of the two otherwinding's, the" armature of between negative 408, to negative battery ZSS, which correspond to conductor 369, resistor 3'11 and battery 3'12 respectively, and this relay 243 will be operated to its right-hand contactandwill interrupt the anode circuit of the left-hand triode section of tube 253. Whenno current is flowing in the lower winding, the armature will be heldon the left-hand contact by current in either one of the other two windings and when current is' flowing in all three windings which is the idle or steady state condition, the

oscillator I is later and two upper windings will overcome the eii e'ct of the lower winding and hold the armature on the left-hand contact. Therelay 243 is provided to prevent a lock-out condition in the event that either one ofthe transmitting relays 218 and 235 fails to respond t6 the last-marking impulse of a series of signal combinationsgreceived by; the receiving relay associated with the opposite side of the repeater. I V

Suppose, for example, that relay 213 has been responding to signals receivedover the linecomprising conductors 21 1 and 2 12 and has been opertheir retransmission into the linecomprising conductors 231 and 232. Sunating relay 236 to efiect pose further that reIayBZB-iails to respond'to the stop impulse of the final code combination before anyinterruption in or cessation of trans mission and remains in the spacing condition. This failure might be due to failure of tube 289 to fire. Accordingly, there" would be no current in the middle winding of relay 243; There would be current in the upper winding because tube 288 has remained. conductive steadily. Relay 213, upon responding to. the finalmarking: impulse, assumed to be the stop impulse, completes the anode circuit of' character timing tube 244. Almost immediately the condenser233 completes its timing-out operation and fires tube 244 which raises the potential of theg'rid- 'o'f theleft hand triode section of tube 253 alio'ngwith thegrid of tube 251 as previously described. As tub 244' becomes conductivdtheflow of anode current through the lower'winding of relay 243 energizes that winding which operates the armature to the I unconnected rig-ht h'and con-tact due to the fact that only the upper of the other two windings of the relay is energized; This interrupts the anode circuit of the left-hand triode section of tube 253 and prevents this section of" the tube from becoming conductive" in response to the raising of the potential of its grid; Accordingly, the flow of direct'current through the inductance winding 212 is prevented, the stopping of the firing potentials to the grids or tubes 2%, 289,

viding a suflicient total magnetic field to restore the armature to the" leftfhandbontacte Upon the restoration of the armature to the left-hand contact, the anode circuit fortheleit-hand triode section of; tu e 2531s completed and this section at once becomes'fconductiveand direct current flows through the inductance winding 212 stop ping the 'oscilla'toryoperation of the resonant circuit. 1 I v Assume now that the relay 243 is not included in the repeater nor any apparatus for-performing "an equivalent function; Under these 'circu rn stances tf'e tube 24'4 upon being fired in response to the stop impulse received over line conductors 211 and 212 would-render the left-hand triode section of tube 23 conductive andianode current would flow whether ornotrel'ay 236 had been operated to marki ng injresponse 'to' the 'stop impulse of marking nature. The anode current in delayed and: the oscillator continues to generate oscillatory potentials, and to ap'pl'y 29 the left-hand triode section of tube 253 would flow through inductance winding 212 and stop the generation of impulses for firing tubes 288, 289, 293 and 294. Relay 236 would remain in the spacin condition interrupting the terminating ,loop for line conductors 231 and 232 through the operating winding of relay 233. A few impulse intervals after response of relay 329 to the final marking impulse received over line conductors 2H and H2, dependent upon the value of condenser 393 and the resistors associated therewith, the spacing bias would be restored to receiving relay 233 and this relay would operate to spacing, in turn operating the relay 3I9 to spacing, quenching tube 244 and restarting the oscillator. The oscillator would be restarted and another series of firing impulses would be applied to the grids of tubes 288, 289, 293 and 294. With relay 233 operated to spacing, the relay 3I9 is also operated to spacing, tube 288 is quenched, the anode circuit of tube 293 is prepared, the spacing bias on relay 2 I3 is changed to marking bias and upon the firing of tube 293 in response to the first timing impulse, relay 2I8 is operated to spacing. At the time of the firing of tube 293' the anode circuit of tube 289 which is presumed to have failed to operate previously is prepared through the upper winding of relay 236 and tube 289 should also fire. If it does relay 236 will be operated to marking and will restore relay 233 to marking which in turn will restore relay 3I9 to marking. Accordingly, the next and all succeed ing pulses transmitted to line conductors 2 I I and 2I2 during the timing out interval of condenser 263 will be marking, and upon the firing of tube 244 by condenser 263 the oscillator will be stopped with both sides of the repeater in the full marking condition. It will be noted that without relay 243, the restoration of relay 236 to marking after it has failed to be operated to that condition in response to the final marking impulse received over line conductors 2H and H2 involves the transmission of at least one spacing signal over line conductors 2H and 2 I2 to the remote station connected thereto whereas with relay 243 included in the system relay 236 is restored to marking condition without the transmission of any signals over line conductors 2I I and 2I2 toward the remote station. Relay 243 has even greater importance to the system when the line circuits terminating in the repeater are arranged for twopath polar operation. Under these circumstances the line conductors 2H and 2 I2 and the line conductors ml and 232 do not terminate in the repeater in loop circuits but have independent terminations for polar operation of the lines. Under these circumstances, relay 233* is operable to spacing solel under the control of a transmitter at a remote station arranged to transmit signals over line conductor 232 and relay 233 will remain in the marking condition even though relay 236 should falsely remain in the spacing condition for an indefinite interval. Thus with relay 236 remaining in the spacing condition, receiving relay 233 will not automatically initiate operations involving the quenching of tube 244, the restarting of the oscillator and the transmission of one or more spacing signals by means of relay 2IB over conductor 2i I, as it will when the line circuits are arranged for neutral operation and relay 236 would remain in the spacing condition until one or the other of the remote station initiated transmission and thereby deactivated tube 244 to restart the oscillator.

It will be noted that the delay in the restoration of spacing bias to the receiving relays 2I3 and 233, afforded by the condensers M6 and 393, respectively, accommodate the function to be performed by the relay 243. The delay of a few impulse intervals prevents the receiving relays from interfering with the extended operation of the oscillator under control of relay 243 independently of a recycling of the timing circuit associated with tube 244. In the heretofore assumed circumstance that relay 236 might not be operated to marking in response to the final marking impulse, if the spacing bias should be restored to relay 233 substantially instantaneously upon the return of relay 329 to marking, and thereupon should relay 233 operate to spacing due to the open condition of the terminating loop of line conductors 215i and 232 at the armature and marking contact of relay 236, tube 244 would be quenched and a complete character timing cycle of condenser 263 would be initiated before relay 243 had an opportunity to assume control over the oscillator for the purpose of efiecting the restoration of relay 236 to marking, and the purpose in providing relay 243 might thereby be defeated.

It will be understood that although the description of the operation of relay 243 was predicated upon an assumed failure of relay 236 to be operated to marking, the relay 243 operates in the same manner and for the same purpose if and when relay 2? fails to be operated to marking upon an interruption in or cessation of transmission into the repeater from the line conductors 23l and 232 for transmission onwardly over line conductors 2H and 2I2.

The repeater is provided with means for transmitting locally generated signals into the lines interconnected by the repeater, this means comprising the transmitting contacts 426. These transmitting contacts are connected to a plug 42? which is insertable into jack 2 Hi. When plug 427 is inserted into jack 2I6, the contacts 426 are inserted into the loop circuit which terminates the line comprising conductors 2H and 2I2. When the transmitting contacts 426 are operated, the terminating loop circuit interconnecting the line conductors 2H and 2| 2 is opened for each spacing signal, thereby transmitting the spacing signals directly into those line conductors without operating transmitting relay 2I8. Since the receiving relay 2 I3 is included in the terminating loop circuit, it responds to spacing and marking signals generated by transmitting contacts 426 in the same manner that it responds to marking and spacing signals received over line conductors 2| I and 2 I2 and these signals are repeated by the regenerative repeater in the manner heretofore described into the telegraph line comprising conductors 23! and 232.

In addition to the tip and sleeve contacts through which the loop circuit terminating line conductors 2H and H2 is adapted to include transmitting contacts 426 when plug 421 is inserted into jack 2I6, the jack has a closed circuit contact associated with the tip spring for closing the line terminating loop circuit of line conductors 2| I and H2 when the plug is not inserted into the jack. Also, jack 2I6 has certain other contacts for adapting transmittin contacts 426, for cooperation with the repeater when the latter is arranged for two-path polar operation by switching means (not shown). The relay 35I is brought under the control of transmitting contacts 426 when the repeater is arranged for twopath polar operation and the armature thereof,

arranged for two-path polar operation.

amps-1 which finds negative battery on its marking contact and positive battery on its spacing contact becomes connected through the uppermost pair of contact springs to a conductorshown as a dotted line 43! in Fig.2 which becomes connected through the switching means (not shown) to the marking contacts of bo'tl-i of the transmitting relays 218 and 23%, the circuits of the opera-ting windings of receiving relays H3 and 233 being.

"of the lines Zil and 23!. Relay 351 is placed under the control of transmitting contacts 426 by rearranging the connections through the switching means (not'shown) so that the operating winding of relay 351 is connected to battery 39! through transmitting contacts 426 and the tip and sleeve terminals of jack 2I6. The-seleetor magnet 38E of the monitoring printer, having its operating circuit extending through the armature and marking contact'of relay 352 to the rightnection to battery 3! through the transmitting contacts 326 when the" repeater circuit is re- Thus when transmitting contacts 4Z B are operated to transmit signals into the two'lines interconnected by the repeater, selector magnet 3-86 of the monitoring printer is operated directly under the control of transmitting contacts 426 along with relay 35!, the relay 352, which'o'p'erates only when the repeater-operatesto regenerate signals, remaining idle.

When signals are being received from one of the telegraph lines-such as that comprising conductors fill and 2l2, and are being transmitted into the other telegraph line which comprises conductors 23I and 232, the transmission may be interrupted at the receiving end by the transmissionof a break signal, which is a steady spacing condition. If the transmission of the break signal is initiated upon 2-32 from the remote station at the time that a spacing signal is being repeated toward that station, the break signal will not become effective because thereceiving'relay 233 is held inmarking condition by the markingbi-as imposed when relay 3% in the spacing condition. Furthermore, the 233 will'not respond to the break signal the instant that relay 329 returns to the marking condition because of the delay inthe removalof the marking bias and the restoration of the spacing bias imposed by condenser 393. The receiving relay 233 will remain in the -marking condition until the relay 2l3 receives a signal combination containing a suiiicient number of successive "marking pulses, during. which the armatures of relays 253 and BZQ'rem'ain ontheir'm-arking-conta'cts, to permit condense-r- 393th time out the Y elay interval for the bias reversal, v'vhereupon the biasing winding will operate relay 2'33 tospa'c- This spacing condition of relay 2 33 will cause the spacing bias onrelay '2 l are be replaced by marking bias, thereby preventing "that relay from operating to spacing, and thebreak:signa1 of spacing nature will be repeated Joy-relay 218 into line conductors-2s: and 232 station connected thereto. Upon the termination of the breakisi gnal, the repeater will return to marking conditi-on, awaitin transmission of signals in either direction.

' --Althoug'h specific embodiments of the invention have been shown in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to specific embodiments but is capable of modification and rearrangement without departing froint'he spirit of the invention and within the :hand terminal of'relay 35I, also receives its conlineconductors 21M and V scope of the appended claims.

What is claimedis: J

1. In a telegraph signal repeater, a signal re- 'sponslv-e relay, a normally inactive impu'lse generator comprising electron discharge means, n'ieans controlled by said relay for setting said generator. in operation, a signal retransmission controlling relay; a pair of electron discharge iti-ibesadapted to have activating potentials simultaneously applied-to their control electrodes by impulse genera-tor andhavin their main space discharge paths associated with oppositely e fioc-tive windings of said signal retransmission eon-trolling relay, and means for selectively com pleting'either of said space discharge paths externally of the tubes according to the operation of said signal responsive relay whereby to ener g-ize one or the other of said oppositely efiective windings of said signal retransmission controlling relay. 9

'2. In a telegraph signal repeater, a relay adapted tooperate to marking or spacing in accordance with incoming signals, a signal retrans mission controlling relay, a pair of electron discharge tubeshaving their main space discharge paths associated with'oppositely effective Windings of said signal retransmission controlling relayancl with the marking and spacing contacts of said first-mentioned relay, means for applying 'activatingpotentials to the control electrodes of said tubes atinte'rvals of unit length telegraph impulses, and'a source of anode potential for said tubes connected to the armature of said firstmentioned relay whereby said tubes are selectively activate'd upon the application'of the activating potentials to their control electrodes and operate said signal retransmission controlling relay correspondingly. 7

3. In -a-telegraph' signal repeater, a relay adaptedto operate to marking or spacing in accordance with incoming signals, a signal retransmission cont-rolling relay, a pairof gas-filledelectron dis tubes are selectively activated upon the applica 7 tion of the activating potentials to their control into-the telegraph lineconiprising conductors-2H andZi 2 as long as the bieak si'g nal retransmitted electrodes and operate said signal retransmission controlling relaycorrespondingly. 7 i. atelegraph repeater, a receiving relay re- ;spon'sive to incoming signals and having an armatore atpositive potential engageable with marking-or spacing contacts of said relay, a relay having oppositelyeffective windings, a pair of electron discharge tubes having their anodes connected through said windingsto said marking and spacat the remote ing contacts, means for momentarily applying activating potentials to the control electrodes of said tubes at intervals of unit length telegraph impulses whereby to activate one or the other of said 5. In a telegraph repeater, a, receiving relay responsive to incoming signals and having an armature at positive potential engageable with marking or spacing contacts of said relay, a relay having oppositely elrective windings, a pair of electron discharge tubes having their anodes connected through said windings to said marking or spacing contacts, means for momentarily applying activating potentials to the control electrodes of said tubes at intervals of unit length telegraph impulses whereby to activate one or the other of said tubes and energize one or the other of said windings, means for holding said second-mentioned relay in either condition established by said oppositely effective windings, and a retransmitting relay controlled by said second-mentioned relay.

6. In a telegraph repeater, a pair of relays responsive to signals received over lines individual to said relays, each of said relays having an armature and marking and spacing contacts, a pair of relays each having a winding energizable in common through the armatures and marking contacts of both of said signal responsive relays and each having a second winding oppositely effective to said first-mentioned windings and energizable individually and selectively through the armature and spacing contact of each of said signal responsive relays, means for holding said second-mentioned relays in either condition established by said oppositely effective windings, and a retransmitting relay controlled by each of said secondmentioned relays.

7. In a telegraph repeater, a pair of relays responsive to signals received overlines individual to said relays, each of said relays having an armature and marking and spacing contacts, a pair of relays each having a winding energizable in common through the armatures and marking contacts f of both of said signal responsive relays and having a second winding oppositely. effective to said first-mentioned winding and energizable individually and selectively through the armature and spacing contact of each of said signal responsive relays, means for holding said second-mentioned relays in either condition established by said oppositely effective windings, a retransmitting relay controlled by each of said second-mentioned relays and means controlled by both of said secondmentioned relays for interrupting the energizing circuit of said first-mentioned windings upon operation of said second-mentioned relays under the control of said windings and for preliminarily preparing said circuit for restoration upon operation of either of said second-mentioned relays under the control of their second-mentioned wind mgs.

8. In a telegraph repeater, a pair of relays responsive to signals received over lines individual to said relays, each of said relays having an armature and marking and spacing contacts, a pair of electron discharge tubes, means for applying activating potentials to the control electrodes of said tubes at intervals of unit length telegraph impulses, a pair of relays each having a winding energizable in common through the armatures and marking contacts of both of said signal responsive relaysv and the discharge path of one of said tubes and having a second winding oppositely 34 elfective to said first-mentioned winding and energizable individually and selectively through the armature and spacing contact of each of said signal responsive relays and the discharge path of the other of said tubes, means for holding said second-mentioned relays in either condition established by said oppositely effective windings, a retransmitting relay controlled by each of said second-mentioned relays, and means controlled by both of said second-mentioned relays for disconnecting the discharge path of one of said tubes from said first-mentioned windings upon operation of said second-mentioned relays under the control of said windings and for recomiecting the discharge path of said tube to said first-mentioned windings upon operation of either of said secondmentioned relays under the control of their second-mentioned windings.

9. In a telegraph repeater, a pair of relays responsive to signals received over lines individual to said relays, each of said relays having an armature and marking and spacing contacts, a source of timing impulses, means including a normally activated electron discharge tube having its discharge path completed serially through the armatures and marking contacts of said relays for disabling said source of timing impulses, a pair of electron discharge tubes adapted to receive activating potentials on their control electrodes from said source of timing impulses, a pair of relays each having a Winding energizable in common through the armatures and marking contacts of both of said signal responsive relays and the discharge path of one of the tubes of said pair of electron discharge tubes and having a second winding oppositely effective to said firstmentioned winding and energizable individually and selectively through the armature and spacing contact of each of said signal responsive relays and the discharge path of the other tube of said pair, means for holding said secondmentioned relays in either condition established by said oppositely effective windings, a retransmitting relay controlled by each of said secondmentioned relays, and switching means controlled by both of said second-mentioned relays for transferring the circuit of the armatures and marking contacts of said signal responsive relays from the discharge path of said one of the tubes of said pair to the discharge path of said first-mentioned tube upon operation of said second-mentioned relays under control of their first-mentioned windings and for reconnecting the circuit of the armatures and marking contacts of said signal responsive relays to the discharge path of said first-mentioned tube.

10. In a telegraph signal repeater, a signal responsive relay, a pair of electron discharge tubes each having a control electrode and a discharge gap, timing means for periodically applying activating potentials to the control electrodes of said tubes, means controlled by said signal responsive relay for selectively completing the discharge gap circuit of one or the other of said tubes externally thereof whereby to control the selective activation of the discharge gap of either tube, and a signal retransmitting relay selectively operable into marking or spacing condition in response to activation of the discharge gap of one or the other of said tubes.

11. In a telegraph signal repeater, a signal responsive relay, a pair of gas-filled electron discharge tubes each having a control electrode and a discharge gap, means controlled by said signal responsive relay for selectively completing the 

